New High Donor Electrolyte for Lithium-Sulfur Batteries

Endowing the Operability of Supercapacitors at High Temperatures by Regulating the Solvation Structure in Dilute Hybrid Electrolyte with Trimethyl Phosphate Cosolvent

The redox stabilities of different oxygen donor solvents (C═O, P═O and S═O) and lithium salt anions for supercapacitors (SCs) electrolytes have been compared by calculating the frontier molecular orbital energy. Among six lithium difluoro(oxalate)borate (LiDFOB)-based mono-solvent electrolytes, the dilute LiDFOB-1,4-butyrolactone (GBL) electrolyte exhibits the highest operating voltage but suffers from electrolyte breakdown at elevated temperatures. Trimethyl phosphate (TMP) exhibits the highest redox stability and a strongly negative electrostatic potential (ESP), making it suitable for promoting the dissolution of LiDFOB as expected. Therefore, TMP is selected as a co-solvent into LiDFOB-GBL electrolyte to regulate Li+ solvation structure and improve the operability of electrolytes at high temperatures. The electrochemical stable potential window (ESPW) of 0.5 m LiDFOB-G/T(5/5) hybrid electrolyte can reach 5.230 V. The activated carbon (AC)-based symmetric SC using 0.5 m LiDFOB-G/T(5/5) hybrid electrolyte achieves a high energy density of 54.2 Wh kg-1 at 1.35 kW kg-1 and the capacitance retention reaches 89.2% after 10 000 cycles. The operating voltage of SC can be maintained above 2 V when the temperature rises to 60 °C.

Development of Electrolytes under Lean Condition in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries stand out as one of the promising candidates for next-generation electrochemical energy storage technologies. A key requirement to realize high-specific-energy Li-S batteries is to implement low amount of electrolyte, often characterized by the electrolyte/sulfur (E/S) ratio. Low E/S ratio aggravates the known challenges for Li-S batteries and introduces new ones originated from the high concentration of polysulfides in limited electrolyte reservoir. In this review, the connections between the fundamental properties of electrolytes and the electrochemical/chemical reactions in Li-S batteries under lean electrolyte condition are elucidated. The emphasis is on how the solvating properties of the electrolyte affect the fate of polysulfides. Built upon the mechanistic analysis, different strategies to design lean electrolytes to improve the overall process of Li-S reactions and Li anode protection are discussed.

Extended Battery Compatibility Consideration from an Electrolyte Perspective

The performance of electrochemical batteries is intricately tied to the physicochemical environments established by their employed electrolytes. Traditional battery designs utilizing a single electrolyte often impose identical anodic and cathodic redox conditions, limiting the ability to optimize redox environments for both anode and cathode materials. Consequently, advancements in electrolyte technologies are pivotal for addressing these challenges and fostering the development of next-generation high-performance electrochemical batteries. This review categorizes perspectives on electrolyte technology into three key areas: additives engineering, comprehensive component analysis encompassing solvents and solutes, and the effects of concentration. By summarizing significant studies, the efficacy of electrolyte engineering is highlighted, and the review advocates for further exploration of optimized component combinations. This review primarily focuses on liquid electrolyte technologies, briefly touching upon solid-state electrolytes due to the former greater vulnerability to electrode and electrolyte interfacial effects. The ultimate goal is to generate increased awareness within the battery community regarding the holistic improvement of battery components through optimized combinations.

Lithium ion Speciation in Cyclic Solvents: Impact of Anion Charge Delocalization and Solvent Polarizability

The increasing demand for lithium batteries has triggered the search for safer and more efficient electrolytes. Insights into the atomistic description of electrolytes are critical for relating microscopic and macroscopic (physicochemical) properties. Previous studies have shown that the type of lithium salt and solvent used in the electrolyte influences its performance by dictating the speciation of the ionic components in the system. Here, we investigate the molecular origins of ion association in lithium-based electrolytes as a function of anion charge delocalization and solvent chemical identity. To this end, a family of cyano-based lithium salts in organic solvents, having a cyclic structure and containing carbonyl groups, was investigated using a combination of linear infrared spectroscopy and ab initio computations. Our results show that the formation of contact-ion pairs (CIPs) is more favorable in organic solvents containing either ester or carbonate groups and in lithium salts with an anion having low charge delocalization than in an amide/urea solvent and an anion with large charge delocalization. Ab initio computations attribute the degree of CIP formation to the energetics of the process, which is largely influenced by the chemical nature of the lithium ion solvation shell. At the molecular level, atomic charge analysis reveals that CIP formation is directly related to the ability of the solvent molecule to rearrange its electronic density upon coordination to the lithium ion. Overall, these findings emphasize the importance of local interactions in determining the nature of ion-molecule interactions and provide a molecular framework for explaining lithium ion speciation in the design of new electrolytes.

Multifunctional Vanadium Nitride-Modified Separator for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are recognized as among the best potential alternative battery systems to lithium-ion batteries and have been widely investigated. However, the shuttle effect has severely restricted the advancement in their practical applications. Here, we prepare vanadium nitride (VN) nanoparticles grown in situ on a nitrogen-doped carbon skeleton (denoted as VN@NC) derived from the MAX phase and use it as separator modification materials for LSBs to suppress the shuttle effect and optimize electrochemical performance. Thanks to the outstanding catalytic performance of VN and the superior electrical conductivity of carbon skeleton derived from MAX, the synergistic effect between the two accelerates the kinetics of both lithium polysulfides (LiPSs) to Li2S and the reverse reaction, effectively suppresses the shuttle effect, and increases cathode sulfur availability, significantly enhancing the electrochemical performance of LSBs. LSBs constructed with VN@NC-modified separators achieve outstanding rate performance and cycle stability. With a capacity of 560 mAh g-1 at 4 C, it exhibits enhanced structural and chemical stability. At 1 C, the device has an incipient capacity of 1052.4 mAh g-1, and the degradation rate averaged only 0.085% over 400cycles. Meanwhile, the LSBs also show larger capacities and good cycling stability at a low electrolyte/sulfur ratio and high surface-loaded sulfur conditions. Thus, a facile and efficient way of preparing modified materials for separators is provided to realize high-performance LSBs.

Releasing Free Anions by High Donor Number Cosolvent in Noncorrosive Electrolytes of Commercially Available Magnesium Salts

Passivation of the magnesium (Mg) anode in the chloride-free electrolytes using commercially available Mg salts is a critical issue for rechargeable Mg batteries. Herein, a high donor number cosolvent of 1-methylimidazolium (MeIm) is introduced into Mg(TFSI)2- and Mg(HMDS)2-based electrolytes to address the passivation problem and realize highly reversible Mg plating/stripping. Theoretical calculations and experimental characterization results reveal that the strong coordination ability of MeIm with Mg2+ can weaken the anion-cation interactions and promote the formation of free anions that have higher reduction stability, thus significantly suppressing anion-derived passivation layer formation. By adding MeIm cosolvent into Mg(TFSI)2-based electrolyte, the average Coulombic efficiency of the Mg//Cu cell is increased from less than 20% to over 90%, and the Mg//Mg cell can stably cycle for over 800 h with a low overpotential. In the MeIm-regulated Mg(HMDS)2-based electrolyte, the solvation structure change, featured by an effective separation of Mg2+ and HMDS-, greatly increases the ionic conductivity by more than 30 times. This solvation structure regulation strategy for noncorrosive electrolytes of commercially available Mg salts has a great potential for application in future rechargeable Mg metal batteries.

Catalytic Effect of Ammonium Thiosulfate as a Bifunctional Electrolyte Additive for Regulating Redox Kinetics in Lithium-Sulfur Batteries by Altering the Reaction Pathway

Sluggish sulfur redox kinetics and incessant shuttling of lithium polysulfides (LiPSs) greatly influence the electrochemical properties of lithium-sulfur (Li-S) batteries and their practical applications. For this reason, ammonium thiosulfate (AMTS) with effective redox regulation capability has been proposed as a functional electrolyte additive to promote the bidirectional conversion of sulfur species and inhibit the shuttle effect of soluble LiPSs. During discharging, the S2O32- in AMTS can trigger the rapid reduction of LiPSs from long chains to short chains by a spontaneous chemical reaction with sulfur species, thereby decreasing the accumulation of LiPSs in the electrolyte. During charging, the NH4+ in the AMTS enhances the dissociation/dissolution of Li2S2/Li2S by hydrogen-binding interactions, which alleviates the electrode surface passivation and facilitates the reversible oxidation of short-chain sulfides back to long chains. The enhanced bidirectional redox kinetics brought about by AMTS endows Li-S cells with high reversible capacity, excellent cycle stability, and rate capability even under lean electrolyte conditions. This work not only illustrates an effective redox regulation strategy by an electrolyte additive but also investigates its catalytic reaction mechanism and Li corrosion behavior. The crucial criteria for screening additives that enable bidirectional redox mediation analogous to AMTS are summarized, and its application perspectives/challenges are further discussed.

Recent advances in electrolyte molecular design for alkali metal batteries

In response to societal developments and the growing demand for high-energy-density battery systems, alkali metal batteries (AMBs) have emerged as promising candidates for next-generation energy storage. Despite their high theoretical specific capacity and output voltage, AMBs face critical challenges related to high reactivity with electrolytes and unstable interphases. This review, from the perspective of electrolytes, analyzes AMB failure mechanisms, including interfacial side reactions, active materials loss, and metal dendrite growth. It then reviews recent advances in innovative electrolyte molecular designs, such as ether, ester, sulfone, sulfonamide, phosphate, and salt, aimed at overcoming the above-mentioned challenges. Finally, we propose the current molecular design principles and future promising directions that can help future precise electrolyte molecular design.

Surface Chemistry of LLZO Garnet Electrolytes with Sulfur in Electron Pair Donor Solvents

Conventional Li-S batteries rely on liquid electrolytes based on LiNO3/DOL/DME mixtures that produce a quasistable interface with the lithium anode. Electron pair donor (EPD) solvents, also known as high donor number solvents, provide much higher polysulfide solubility and close-to-ideal sulfur utilization, making them solvents of choice for lean electrolyte Li-S cells. However, their instability to reduction requires incorporation of an ion-conductive membrane that is stable with Li-such as garnet LLZO and also stable with sulfur/polysulfides. We report that even trace amounts of LiOH on a LLTZO surface trigger a complex reaction with sulfur dissolved in typical EPD solvents (i.e., N,N-dimethylacetamide, DMA) to produce a highly resistive impedance layer that quickly grows with time from 1000 to 10,000 Ω cm2 over a few hours, thus impeding Li+ transport across the interface. Decorating the LLZO with protective phosphate groups to produce a modified surface provides a very low charge-transfer resistance of 40 Ω cm2 that is maintained over time and inhibits the reaction of LiOH and dissolved sulfur. Hybrid liquid-solid electrolyte cells constructed on this concept result in a high sulfur utilization of 1400 mAh g-1 which is 85% of theoretical and remains constant over cycling even with conventional, unoptimized carbon/sulfur cathodes.

Correlating Polysulfide Solvation Structure with Electrode Kinetics towards Long-Cycling Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are promising due to ultrahigh theoretical energy density. However, their cycling lifespan is crucially affected by the electrode kinetics of lithium polysulfides. Herein, the polysulfide solvation structure is correlated with polysulfide electrode kinetics towards long-cycling Li-S batteries. The solvation structure derived from strong solvating power electrolyte induces fast anode kinetics and rapid anode failure, while that derived from weak solvating power electrolyte causes sluggish cathode kinetics and rapid capacity loss. By contrast, the solvation structure derived from medium solvating power electrolyte balances cathode and anode kinetics and improves the cycling performance of Li-S batteries. Li-S coin cells with ultra-thin Li anodes and high-S-loading cathodes deliver 146 cycles and a 338 Wh kg-1 pouch cell undergoes stable 30 cycles. This work clarifies the relationship between polysulfide solvation structure and electrode kinetics and inspires rational electrolyte design for long-cycling Li-S batteries.

A Radical Pathway and Stabilized Li Anode Enabled by Halide Quaternary Ammonium Electrolyte Additives for Lithium-Sulfur Batteries

Passivation of the sulfur cathode by insulating lithium sulfide restricts the reversibility and sulfur utilization of Li-S batteries. 3D nucleation of Li2 S enabled by radical conversion may significantly boost the redox kinetics. Electrolytes with high donor number (DN) solvents allow for tri-sulfur (S3 ⋅- ) radicals as intermediates, however, the catastrophic reactivity of such solvents with Li anodes pose a great challenge for their practical application. Here, we propose the use of quaternary ammonium salts as electrolyte additives, which can preserve the partial high-DN characteristics that trigger the S3 ⋅- radical pathway, and inhibit the growth of Li dendrites. Li-S batteries with tetrapropylammonium bromide (T3Br) electrolyte additive deliver the outstanding cycling stability (700 cycles at 1 C with a low-capacity decay rate of 0.049 % per cycle), and high capacity under a lean electrolyte of 5 μLelectrolyte  mgsulfur -1 . This work opens a new avenue for the development of electrolyte additives for Li-S batteries.

Tuning and Balancing the Donor Number of Lithium Salts and Solvents for High-Performance Li Metal Anode

The low reversibility of Li deposition/stripping in conventional carbonate electrolytes hinders the development of lithium metal batteries. Herein, we proposed a combination of solvents with a moderate donor number (DN) and LiNO3 as the sole salt, which has rarely been attempted due to its low solubility or dissociation degree in common solvents. It is found that the DN value of solvents is highly correlated to the reversibility of Li deposition behavior when LiNO3 is applied as the sole salt. The combination of LiNO3 and solvents with moderate DN behaves like a quasi-concentrated electrolyte even at a common or moderate concentration, while neither the solvents with poor solubility and low dissociation for LiNO3 (which usually corresponds to a low DN) nor the solvents with high dissociation for LiNO3 (which usually corresponds to an overly high DN) can achieve a high reversibility for low conductivity or excessive solvent decomposition. As a result, a Coulombic efficiency as high as 99.6% for Li deposition/stripping is achieved with the optimized combination. We believe this work will give a better understanding of the role of anions and solvents in the regulation of the solvation structure, and DN can be utilized as an important guideline to sieve suitable solvents for LiNO3 as the main salt to exhibit intriguing properties beyond traditional cognition.

Guiding maps of solvents for lithium-sulfur batteries via a computational data-driven approach

Practical realization of lithium-sulfur batteries requires designing optimal electrolytes with controlled dissolution of polysulfides, high ionic conductivity, and low viscosity. Computational chemistry techniques enable tuning atomistic interactions to discover electrolytes with targeted properties. Here, we introduce ComBat (Computational Database for Lithium-Sulfur Batteries), a public database of ∼2,000 quantum-chemical and molecular dynamics properties for lithium-sulfur electrolytes composed of solvents spanning 16 chemical classes. We discuss the microscopic origins of polysulfide clustering and the diffusion mechanism of electrolyte components. Our findings reveal that polysulfide solubility cannot be determined by a single solvent property like dielectric constant. Rather, observed trends result from the synergistic effect of multiple factors, including solvent C/O ratio, fluorination degree, and steric hindrance effects. We propose binding energy as a proxy for Li+ dissociation, which is a property that impacts the ionic conductivity. The insights obtained in this work can serve as guiding maps to design optimal lithium-sulfur electrolyte compositions.

Electrolytes with moderate lithium polysulfide solubility for high-performance long-calendar-life lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with high energy density and low cost are promising for next-generation energy storage. However, their cycling stability is plagued by the high solubility of lithium polysulfide (LiPS) intermediates, causing fast capacity decay and severe self-discharge. Exploring electrolytes with low LiPS solubility has shown promising results toward addressing these challenges. However, here, we report that electrolytes with moderate LiPS solubility are more effective for simultaneously limiting the shuttling effect and achieving good Li-S reaction kinetics. We explored a range of solubility from 37 to 1,100 mM (based on S atom, [S]) and found that a moderate solubility from 50 to 200 mM [S] performed the best. Using a series of electrolyte solvents with various degrees of fluorination, we formulated the Single-Solvent, Single-Salt, Standard Salt concentration with Moderate LiPSs solubility Electrolytes (termed S6MILE) for Li-S batteries. Among the designed electrolytes, Li-S cells using fluorinated-1,2-diethoxyethane S6MILE (F4DEE-S6MILE) showed the highest capacity of 1,160 mAh g-1 at 0.05 C at room temperature. At 60 °C, fluorinated-1,4-dimethoxybutane S6MILE (F4DMB-S6MILE) gave the highest capacity of 1,526 mAh g-1 at 0.05 C and an average CE of 99.89% for 150 cycles at 0.2 C under lean electrolyte conditions. This is a fivefold increase in cycle life compared with other conventional ether-based electrolytes. Moreover, we observed a long calendar aging life, with a capacity increase/recovery of 4.3% after resting for 30 d using F4DMB-S6MILE. Furthermore, the correlation between LiPS solubility, degree of fluorination of the electrolyte solvent, and battery performance was systematically investigated.

Insights into the solvation chemistry in liquid electrolytes for lithium-based rechargeable batteries

Lithium-based rechargeable batteries have dominated the energy storage field and attracted considerable research interest due to their excellent electrochemical performance. As indispensable and ubiquitous components, electrolytes play a pivotal role in not only transporting lithium ions, but also expanding the electrochemical stable potential window, suppressing the side reactions, and manipulating the redox mechanism, all of which are closely associated with the behavior of solvation chemistry in electrolytes. Thus, comprehensively understanding the solvation chemistry in electrolytes is of significant importance. Here we critically reviewed the development of electrolytes in various lithium-based rechargeable batteries including lithium-metal batteries (LMBs), nonaqueous lithium-ion batteries (LIBs), lithium-sulfur batteries (LSBs), lithium-oxygen batteries (LOBs), and aqueous lithium-ion batteries (ALIBs), and emphasized the effects of interactions between cations, anions, and solvents on solvation chemistry, and functions of solvation chemistry in different types of electrolytes (strong solvating electrolytes, moderate solvating electrolytes, and weak solvating electrolytes) on the electrochemical performance and redox mechanism in the abovementioned rechargeable batteries. Specifically, the significant effects of solvation chemistry on the stability of electrode-electrolyte interphases, suppression of lithium dendrites in LMBs, inhibition of the co-intercalation of solvents in LIBs, improvement of anodic stability at high cut-off voltages in LMBs, LIBs and ALIBs, regulation of redox pathways in LSBs and LOBs, and inhibition of hydrogen/oxygen evolution reactions in LOBs are thoroughly summarized. Finally, the review concludes with a prospective outlook, where practical issues of electrolytes, advanced in situ/operando techniques to illustrate the mechanism of solvation chemistry, and advanced theoretical calculation and simulation techniques such as "material knowledge informed machine learning" and "artificial intelligence (AI) + big data" driven strategies for high-performance electrolytes have been proposed.

Confronting Sulfur Electrode Passivation and Li Metal Electrode Degradation in Lithium-Sulfur Batteries Using Thiocyanate Anion

Salt anions with a high donor number (DN) enable high sulfur utilization in lithium-sulfur (Li-S) batteries by inducing three-dimensional (3D) Li₂ S growth. However, their insufficient compatibility with Li metal electrodes limits their cycling stability. Herein, a new class of salt anion, thiocyanate (SCN^- ), is presented, which features a Janus character of electron donor and acceptor. Due to a strong Li⁺ coordination by SCN^- and the direct interaction of SCN^- with polysulfide anions, the LiSCN electrolyte has a remarkably high lithium polysulfide solubility. This electrolyte induces 3D Li₂ S formation and ameliorates cathode passivation, even more than Br^- , a typical high DN anion. Moreover, SCN^- forms a Li₃ N-enriched stable SEI layer at the surface of the Li metal electrode, enhancing cycling stability. A Li-S battery with the LiSCN electrolyte shows high current density operation (2.54 mA cm⁻² ) with high discharge capacity (1133 mAh g⁻¹ ) and prolonged cycle life (100 cycles). This work demonstrates that the cathode and anode performance in a Li-S battery can be simply and concurrently enhanced by the single salt anion.

The Polysulfide-Cathode Binding Energy Landscape for Lithium Sulfide Growth in Lithium-Sulfur Batteries

A cathode substrate with strong adsorption of lithium polysulfides (LiPSs) has been preferred for lithium-sulfur (Li-S) batteries. However, the recent finding that controlled growth of lithium sulfides (Li₂ S) during discharge is crucial for S utilization stimulates improvement of this preference. Here, the Li₂ S growth and cell capacity in the LiPS binding energy landscape of cathode substrates are investigated. Specifically, Co-based ternary oxides are employed to obtain binding energies in the range of 4.0-7.4 eV. Of these substrates, only the MnCo₂ O₄ substrate with moderate LiPS affinity exhibits 3D Li₂ S growth. The MnCo₂ O₄ cells achieve high sulfur utilization up to 84% at 0.2 C and excellent performance even under high sulfur loading/lean electrolyte conditions. In contrast, weak affinity substrates such as ZnCo₂ O₄ and strong affinity substrates such as NiCo₂ O₄ and CuCo₂ O₄ exhibit low discharge capacity with 2D Li₂ S growth. For optimal LiPS affinity driving 3D growth, a balance between promoting LiPS adsorption and diffusion limitation in the LiPS adsorption layer is suggested.

A Review on Regulating Li+ Solvation Structures in Carbonate Electrolytes for Lithium Metal Batteries

Lithium metal batteries (LMBs) are considered promising candidates for next-generation battery systems due to their high energy density. However, commercialized carbonate electrolytes cannot be used in LMBs due to their poor compatibility with lithium metal anodes. While increasing cut-off voltage is an effective way to boost the energy density of LMBs, conventional ethylene carbonate-based electrolytes undergo a number of side reactions at high voltages. It is therefore critical to upgrade conventional carbonate electrolytes, the performance of which is highly influenced by the solvation structure of lithium ions (Li⁺ ). This review provides a comprehensive overview of the strategies to regulate the solvation structure of Li⁺ in carbonate electrolytes for LMBs by better understanding the science behind the Li⁺ solvation structure and Li⁺ behavior. Different strategies are systematically compared to help select better electrolytes for specific applications. The remaining scientific and technical problems are pointed out, and directions for future research on carbonate electrolytes for LMBs are proposed.

High Energy Density Lithium-Sulfur Batteries Based on Carbonaceous Two-Dimensional Additive Cathodes

The increasing demand for electrical energy storage makes it essential to explore alternative battery chemistries that overcome the energy-density limitations of the current state-of-the-art lithium-ion batteries. In this scenario, lithium-sulfur batteries (LSBs) stand out due to the low cost, high theoretical capacity, and sustainability of sulfur. However, this battery technology presents several intrinsic limitations that need to be addressed in order to definitively achieve its commercialization. Herein, we report the fruitfulness of three different formulations using well-selected functional carbonaceous additives for sulfur cathode development, an in-house synthesized graphene-based porous carbon (ResFArGO), and a mixture of commercially available conductive carbons (CAs), as a facile and scalable strategy for the development of high-performing LSBs. The additives clearly improve the electrochemical properties of the sulfur electrodes due to an electronic conductivity enhancement, leading to an outstanding C-rate response with a remarkable capacity of 2 mA h cm^-2 at 1C and superb capacities of 4.3, 4.0, and 3.6 mA h cm^-2 at C/10 for ResFArGO₁₀, ResFArGO₅, and CAs, respectively. Moreover, in the case of ResFArGO, the presence of oxygen functional groups enables the development of compact high sulfur loading cathodes (>4 mg_S cm^-2) with a great ability to trap the soluble lithium polysulfides. Notably, the scalability of our system was further demonstrated by the assembly of prototype pouch cells delivering excellent capacities of 90 mA h (ResFArGO₁₀ cell) and 70 mA h (ResFArGO₅ and CAs cell) at C/10.

Unveiling light effect on formation of trisulfur radicals in lithium-sulfur batteries

is the important electrochemical intermediate in Li-S batteries of highly solvating solvents. Herein, the dissociation of into is deeply studied. light is proven to promote the formation of from the dissociation of . Accordingly, a strategy of pre-introducing highly active into DMSO-based electrolyte is proposed to activate sulfur cathodes of Li-S batteries.

n-Hexane Diluted Electrolyte with Ultralow Density enables Li-S Pouch Battery Toward >400 Wh kg-1

Lithium-sulfur (Li-S) batteries are attractive candidates for next generation energy storage devices due to their high theoretical energy density of up to 2600 Wh kg^-1 . However, the uneven deposition of lithium, the undesired shuttle of lithium polysulfides (LiPSs), and the excess weight fraction of electrolyte severely impair the practical energy density of Li-S batteries. Here, a low concentrated and nonpolar n-hexane (NH)-diluted electrolyte (named as LCDE) with ultralow-density to alleviate the above dilemmas is proposed. The nonpolar NH boosts the diffusion of lithium ion in LCDE, favoring the homogeneous deposition of lithium. This nonpolar effect also reduces the solubilities of LiPSs, promoting a quasi-solid-state transformation of sulfur chemistry, thus tremendously eradicating the shuttle of LiPSs. Most importantly, the ultra-light NH diluent enables the LCDE with an ultralow density of only 0.79 g mL^-1 , which reduces the weight of LCDE by 32.5% compared with conventional ether-based electrolyte. Owing to all the merits, the Li-S pouch cell achieves a high energy density up to 417 Wh kg^-1 . The nonpolar NH-diluted electrolyte with multifunction presented in this work provides a new and feasible direction to increase the practical energy density of Li-S batteries.

Functional CNTs@EMIM+ -Br- Electrode Enabling Polysulfides Confining and Deposition Regulating for Solid-State Li-Sulfur Battery

With an extremely high theoretical energy density, poly(ethylene oxide) (PEO)-based solid-state lithium-sulfur (Li-S) batteries are emerging as one of the most feasible and safest battery storage systems. However, the long-term cycling performance is severely impeded by polysulfides (Li₂ S_n , n = 4-8) shuttling and terrible electrode passivation from the electronic insulating Li₂ S. Here, a novel cathode through chemically grafted 1-Ethyl-3-methylimidazolium bromide (EMIM⁺ -Br^- ) to carbon nanotube (CNTs) for PEO-based Li-S batteries is reported (CNTs@EMIM-Br/S). Concretely, bi-functional mediator EMIM⁺ -Br^- not only inhibits the polysulfides shuttling by strong chemical interactions via EMIM⁺ , but also facilitates the electrochemical kinetics for promoting the formation of 3D particulate Li₂ S through high donor anion (Br^- ). Satisfactorily, dual-function CNTs@EMIM-Br/S cathode exhibits high sulfur utilization with the capacity of up to 1298 mAh g^-1 , and keeps high capacity retention of 80.2% at 0.2 C after 350 cycles, exceeding that of many reported PEO-based solid-state Li-S batteries. This work will open a new door for rationally designed architecture to enable the practical applications of advanced Li-S batteries.

Unraveling the Atomic-Level Manipulation Mechanism of Li2 S Redox Kinetics via Electron-Donor Doping for Designing High-Volumetric-Energy-Density, Lean-Electrolyte Lithium-Sulfur Batteries

Designing dense thick sulfur cathodes to gain high-volumetric/areal-capacity lithium-sulfur batteries (LSBs) in lean electrolytes is extremely desired. Nevertheless, the severe Li₂ S clogging and unclear mechanism seriously hinder its development. Herein, an integrated strategy is developed to manipulate Li₂ S redox kinetics of CoP/MXene catalyst via electron-donor Cu doping. Meanwhile a dense S/Cu_0.1 Co_0.9 P/MXene cathode (density = 1.95 g cm^-3 ) is constructed, which presents a large volumetric capacity of 1664 Ah L^-1 (routine electrolyte) and a high areal capacity of ≈8.3 mAh cm^-2 (lean electrolyte of 5.0 µL mg_s ^-1 ) at 0.1 C. Systematical thermodynamics, kinetics, and theoretical simulation confirm that electron-donor Cu doping induces the charge accumulation of Co atoms to form more chemical bonding with polysulfides, whereas weakens CoS bonding energy and generates abundant lattice vacancies and active sites to facilitate the diffusion and catalysis of polysulfides/Li₂ S on electrocatalyst surface, thereby decreasing the diffusion energy barrier and activation energy of Li₂ S nucleation and dissolution, boosting Li₂ S redox kinetics, and inhibiting shuttling in the dense thick sulfur cathode. This work deeply understands the atomic-level manipulation mechanism of Li₂ S redox kinetics and provides dependable principles for designing high-volumetric-energy-density, lean-electrolyte LSBs through integrating bidirectional electro-catalysts with manipulated Li₂ S redox and dense-sulfur engineering.

Ultra-Low Concentration Electrolyte Enabling LiF-Rich SEI and Dense Plating/Stripping Processes for Lithium Metal Batteries

The interface structure of the electrode is closely related to the electrochemical performance of lithium-metal batteries (LMBs). In particular, a high-quality solid electrode interface (SEI) and uniform, dense lithium plating/stripping processes play a key role in achieving stable LMBs. Herein, a LiF-rich SEI and a uniform and dense plating/stripping process of the electrolyte by reducing the electrolyte concentration without changing the solvation structure, thereby avoiding the high cost and poor wetting properties of high-concentration electrolytes are achieved. The ultra-low concentration electrolyte with an unchanged Li⁺ solvation structure can restrain the inhomogeneous diffusion flux of Li⁺ , thereby achieving more uniform lithium deposition and stripping processes while maintaining a LiF-rich SEI. The LiIICu battery with this electrolyte exhibits enhanced cycling stability for 1000 cycles with a coulombic efficiency of 99% at 1 mA cm^-2 and 1 mAh cm^-2 . For the LiIILiFePO₄ pouch cell, the capacity retention values at 0.5 and 1 C are 98.6% and 91.4%, respectively. This study offers a new perspective for the commercial application of low-cost electrolytes with ultra-low concentrations and high concentration effects.

Sacrificial Template Method to Synthesize Atomically Dispersed Mn Atoms on S, N-Codoped Carbon as a Separator Modifier for Advanced Li-S Batteries

Efficient and durable electrocatalysts are important for polysulfide conversion in high-performance Li-S batteries. Herein, we report a sacrificial template strategy to synthesize a sulfur/nitrogen-codoped carbon-supported manganese (Mn) single-atom catalyst (Mn/SNC). The synthesis is enabled by fabricating a novel precursor, i.e., cadmium sulfide (CdS) wrapped with Mn ion-impregnated polyporrole (CdS@Mn-PPy), and subsequent pyrolysis. During pyrolysis, the CdS template is decomposed into Cd and S, PPy-derived carbon is doped with N and S, and Mn ions are reduced to Mn atoms, forming Mn-N active sites. The evaporation of Cd atoms/clusters creates abundant pores in the carbon substrate to expose the active sites and facilitate ion transport, and S atoms can form edge C-S-C bonds to improve the activity of Mn-N sites. Benefiting from the above advantages, the Mn/SNC catalyst markedly enhances the performance of Li-S batteries, delivering an initial capacity of 1563.7 mAh g^-1 at 0.1C, a capacity decay of only 0.037% per cycle after 1600 cycles at 2C; a capacity of 1045.1 mAh g^-1 at a high sulfur loading of 7.44 mg cm^-2 at 0.2C, and a capacity retention of 73.1% after 180 cycles. This work provides a strategy that may benefit further the rational design and development of single-atom catalysts for application in renewable energy.

Novel Urea-Based Molecule Functioning as a Solid Electrolyte Interphase Enabler and LiPF6 Decomposition Inhibitor for Fast-Charging Lithium Metal Batteries

The practical application of lithium metal batteries is impeded by the growth of dendrites and decomposition of electrolytes especially at high temperature in normal carbonate-based electrolytes. Herein, a novel urea-based molecule, 1,3-dimethyl-2-imidazolidinone (DMI), with a high donor number is proposed, which exhibits an extraordinary solubility of LiNO₃ of over 5 M. As a result, a sufficient amount of LiNO₃ is readily introduced into the carbonate electrolytes with DMI as an additive, and an average coulombic efficiency of 99.1% for lithium plating/stripping is achieved due to a stable solid electrolyte interphase (SEI) rich in inorganic-rich lithium salts. The Li||Li symmetric cell achieves a stable operation for over 2500 h at 0.5 mA cm^-2 and 1 mAh cm^-2, and a granular shape of deposited Li metal is still preserved even at a high current density of 10 mA cm^-2. Besides, the decomposition of LiPF₆ is inhibited benefiting from its enhanced dissociation after the addition of DMI/LiNO₃ and DMI's function as a PF₅ scavenger. Consequently, the Li||LiFePO₄ cell succeeds to achieve an excellent capacity retention of 95.6% after 2200 cycles at a high rate of 5C, and a stable operation is realized at a high temperature of 60 °C even under harsh conditions (45 μm ultrathin Li and ∼1.5 mAh cm^-2 LiFePO₄). This work enriches the solvents and additives pool for stable and high-performance lithium metal batteries and will shed light on future developments of advanced battery electrolytes.

Deciphering the role of LiNO3 additives in Li-S batteries

The ultrahigh theoretical energy density of lithium-sulfur (Li-S) batteries has attracted intensive research interest. However, most of the long-term cycling performance parameters are strongly dependent on the utilization of the electrolyte, which is considered as an indispensable component in Li-S batteries. Over the past few decades, numerous research studies around LiNO₃ as an electrolyte additive have been carried out and have been confirmed to significantly upgrade the electrochemical performance of Li-S batteries, but the mechanism of performance improvement is still not well-understood. In this minireview, we revisit the controversial issues surrounding LiNO₃ based on recent representative studies, provide a comprehensive understanding of the role of LiNO₃ in the Li-S battery system, and specifically discuss what the panoramic view of the solid electrolyte interface film formed by LiNO₃ on the surface of Li metal anodes looks like. Finally, we present general conclusions and unique insights into the future development of Li-S batteries. This minireview aims to provide a tutorial reference for researchers who are ready to enter or are active in the field of Li-S batteries.

Discovery of Dual-Functional Amorphous Titanium Suboxide to Promote Polysulfide Adsorption and Regulate Sulfide Growth in Li-S Batteries

Lithium-sulfur (Li-S) batteries are promising as next-generation energy storage systems. Adsorbents for sulfide species are favorably applied to the cathode, but this substrate often results in a surface-passivating lithium sulfide(Li₂ S) film with a strong adsorption of Li₂ S. Here, an amorphous titanium suboxide (a-TiOx) is presented that strongly adsorbs lithium polysulfides (Li₂ S_x , x < 6) but relatively weakly adsorbs to Li₂ S. With these characteristics, the a-TiO_x achieves high conversion of Li₂ S_x and high sulfur utilization accompanying the growth of particulate Li₂ S. The DFT calculations present a mechanism for particulate growth driven by the promoted diffusion and favorable clustering of Li₂ S. The a-TiO_x -coated carbon nanotube-assembled film (CNTF) cathode substrate cell achieves a high discharge capacity equivalent to 90% sulfur utilization at 0.2 C. The cell also delivers a high capacity of 850 mAh g^-1 even at the ultra-high-speed of 10 C and also exhibits high stability of capacity loss of 0.0226% per cycle up to 500 cycles. The a-TiO_x /CNTF is stacked to achieve a high loading of 7.5 mg S cm^-2 , achieving a practical areal capacity of 10.1 mAh cm^-2 .

Electrode Interface Engineering in Lithium-Sulfur Batteries Enabled by a Trifluoroacetamide-Based Electrolyte

The passivation caused by the deposition of the insulating discharge final product, lithium sulfide (Li₂S), leads to the instability of the cycle and the rapid capacity fading of lithium-sulfur batteries (LSBs), which restricts the development of LSBs. This paper proposes the employment of trifluoroacetamide (TFA) as an electrolyte additive to alleviate the passivation by increasing the solubility of Li₂S. The solubilization effect of TFA on Li₂S is attributed to intermolecular hydrogen bonds and O-Li bonds. Li₂S in the TFA-based electrolyte exhibits a flower-like 3D deposition behavior, which further alleviates the surface passivation of the electrode and impels conversion kinetics. In addition, the LiF-rich solid electrolyte interface layer can effectively defend the Li metal anode and suppress the growth of Li dendrites. Accordingly, the discharge capacity of the TFA-based battery remains at an excellent 681.2 mA h g^-1 after 400 cycles with a Coulombic efficiency of 99% at 0.5 C. After the battery stabilizes, the capacity decay is only 0.036% per cycle. Under harsh conditions, such as high rates (2 C) and high sulfur loadings (5.2 mg cm^-2) with lean electrolytes and elevated temperatures (60 °C), TFA-containing batteries exhibited more durable and stable cycling. This paper provides new insights into solving practical problems and gives an impetus in cycle stability for LSBs.

Balancing Electrolyte Donicity and Cathode Adsorption Capacity for High-Performance LiS Batteries

LiS batteries with high theoretical capacity are attracting attention as next-generation energy storage systems. Much effort has been devoted to the introduction of cathode materials with strong adsorption to sulfide species, but it is presented that this selection should be refined in the application of high donicity electrolytes. The oxides with different adsorption capacities are explored while controlling the electrolyte donicity, confirming the trade-off effect between the donicity and the adsorption capacity for sulfur conversion. Specifically, a cathode substrate containing oxide nanoparticles of MgO, NiO, Fe₂ O₃ , Co₃ O₄ , and V₂ O₅ is prepared with spectra in adsorption capacity as well as low and high donicity electrolytes by controlling the concentration of LiNO₃ salt. Strong adsorbent oxides such as Co₃ O₄ and V₂ O₅ cause competitive adsorption of electrolyte salts in high donicity electrolytes, resulting in poor cell performance. High cell performance is achieved on weakly adsorbing oxides of MgO or NiO with high donicity electrolytes; the MgO-containing cathode cell delivers a high discharge capacity of 1394 mAh g^-1 at 0.2 C. It is believed that understanding the interactions between electrolytes and adsorbent substrates will be the cornerstone of high-performance LiS batteries.

Electrolyte Solvation Chemistry for the Solution of High-Donor-Number Solvent for Stable Li-S Batteries

Passivation of the sulfur electrode by insulating lithium sulfide (Li₂ S) restricts the reversibility and sulfur utilization of lithium-sulfur (Li-S) batteries. Although electrolytes with high donor number (DN) solvents induce tri-sulfur radical intermediate thus 3D nucleation of Li₂ S with fast kinetics can be achieved, their catastrophic reactivities with Li metal hinder practical applications. Here, the use of high DN solvent as an additive instead of as co-solvent to solve their incompatibility between cathode and anode is proposed, by adopting N-methyl-2-pyrrolidone (NMP) as a proof-of-concept. Such a strategy is accomplished by the unique solvation structure of the NMP added electrolyte, where the preference of NMP-Li⁺ coordination squeezes out partial 1,2-dimethoxyethane (DME) molecules while enriching 1,3-dioxolane (DOL) molecules in the first solvation sheath of Li⁺ ions. It affords the robust SEI on Li metal from corrosion either by NMP or the dissolved polysulfides. Spectral analyses (Raman and UV-vis) also verify that the coordinated NMP additive preserves its S₃ ^•- radicals stabilization ability as it does as a co-solvent, which effectively improves the sulfur conversion kinetics and reversibility. This approach enables competitive capacity retention and a stable cycling performance of 340 cycles, which is one of the longest lifespans known for the high DN solvent involved Li-S batteries.

A Facile Pre-Lithiated Strategy towards High-Performance Li2Se-LiTiO2 Composite Cathode for Li-Se Batteries

Conventional lithium-ion batteries with a limited energy density are unable to assume the responsibility of energy-structure innovation. Lithium-selenium (Li-Se) batteries are considered to be the next generation energy storage devices since Se cathodes have high volumetric energy density. However, the shuttle effect and volume expansion of Se cathodes severely restrict the commercialization of Li-Se batteries. Herein, a facile solid-phase synthesis method is successfully developed to fabricate novel pre-lithiated Li₂Se-LiTiO₂ composite cathode materials. Impressively, the rationally designed Li₂Se-LiTiO₂ composites demonstrate significantly enhanced electrochemical performance. On the one hand, the overpotential of Li₂Se-LiTiO₂ cathode extremely decreases from 2.93 V to 2.15 V. On the other hand, the specific discharge capacity of Li₂Se-LiTiO₂ cathode is two times higher than that of Li₂Se. Such enhancement is mainly accounted to the emergence of oxygen vacancies during the conversion of Ti⁴⁺ into Ti³⁺, as well as the strong chemisorption of LiTiO₂ particles for polyselenides. This facile pre-lithiated strategy underscores the potential importance of embedding Li into Se for boosting electrochemical performance of Se cathode, which is highly expected for high-performance Li-Se batteries to cover a wide range of practical applications.

Boosting the Energy Density of Li||CFx Primary Batteries Using a 1,3-Dimethyl-2-imidazolidinone-Based Electrolyte

Elevating the discharge voltage plateau is regarded as the most effective strategy to improve the energy density of Li||CF_x batteries in consideration of the finite capacity of CF_x (x ∼ 1) cathodes. Here, an electrolyte, with LiBF₄ in 1,3-dimethyl-2-imidazolidinone (DMI)/1,2-dimethoxyethane (DME), is developed for the first time to substantially promote the discharge voltage of CF_x without compromising the available discharge capacity. DME possesses the property of low viscosity, while DMI functions to increase the voltage plateau during discharge owing to its moderate nucleophilicity and donor number, which decreases the energy barrier for breaking C-F bonds. The optimized electrolyte exhibits a significantly high average discharge voltage of 2.69 V at a current density of 10 mA g^-1, which is 11.6% higher than the control electrolyte (2.41 V). In addition, a high energy density of 2099 Wh kg^-1 is achieved in the optimized electrolyte (vs 1905 Wh kg^-1 in the control electrolyte), showing great potential for practical applications.

Enthalpies of Adduct Formation between Boron Trifluoride and Selected Organic Bases in Solution: Toward an Accurate Theoretical Entry to Lewis Basicity

The Lewis basicity of selected organic bases, modeled by the enthalpies of adduct formation between gaseous BF₃ and bases in dichloromethane (DCM) solution, is critically examined. Although experimental enthalpies for a large number of molecules have been reported in the literature, it may be desirable to estimate missing or uncertain data for important Lewis bases. We decided to use high-level ab initio procedures, combined with a polarized continuum solvation model, in which the solvated species were the clusters formed by specific hydrogen bonding of DCM with the Lewis base and the Lewis base/BF₃ adduct. This mode of interaction with DCM corresponds to a specific solvation model (SSM). The results essentially showed that the enthalpy of BF₃ adduct formation in DCM solution was clearly influenced by specific interactions, with DCM acting as hydrogen-bonding donor (HBD) molecule in two ways: base/DCM and adduct/DCM, confirming that specific solvation is an important contribution to experimentally determined Lewis basicity scales. This analysis allowed us to conclude that there are reasons to suspect some gas-phase values to be in error by more than the stated experimental uncertainty. Some experimental values in DCM solution that were uncertain for identified reasons could be complemented by the computed values.

High-performance lithium-sulfur batteries enabled by regulating Li2S deposition

Lithium-sulfur batteries (LSBs) have received intensive attention in recent years due to their high theoretical energy density derived from the lithiation of sulfur. In the discharge process, sulfur transforms into lithium polysulfides (LiPSs) that dissolve in liquid electrolytes and then into insoluble Li₂S precipitated on the electrode surface. The electronically and ionically insulating Li₂S leads to two critical issues, including the sluggish reaction kinetics from LiPSs to Li₂S and the passivation of the electrode. In this regard, controlling the Li₂S deposition is significant for improving the performance of LSBs. In this perspective, we have summarized the recent achievements in regulating the Li₂S deposition to enhance the performance of LSBs, including the solution-mediated growth of Li₂S, sulfur host enhanced nucleation and catalysis induced kinetic improvement. Moreover, the challenges and possibilities for future research studies are discussed, highlighting the significance of regulating the Li₂S deposition to realize the high electrochemical performance and promote the practical uses of LSBs.

Binder-free and high-loading sulfurized polyacrylonitrile cathode for lithium/sulfur batteries

Sulfurized polyacrylonitrile (SPAN) is a promising active material for Li/S batteries owing to its high sulfur utilization and long-term cyclability. However, because SPAN electrodes are synthesized using powder, they require large amounts of electrolyte, conducting agents, and binder, which reduces the practical energy density. Herein, to improve the practical energy density, we fabricated bulk-type SPAN disk cathodes from pressed sulfur and polyacrylonitrile powders using a simple heating process. The SPAN disks could be used directly as cathode materials because their π–π structures provide molecular-level electrical connectivity. In addition, the electrodes had interconnected pores, which improved the mobility of Li⁺ ions by allowing homogeneous adsorption of the electrolyte. The specific capacity of the optimal electrode was very high (517 mA h g_electrode⁻¹). Furthermore, considering the weights of the anode, separator, cathode, and electrolyte, the Li/S cell exhibited a high practical energy density of 250 W h kg⁻¹. The areal capacity was also high (8.5 mA h cm⁻²) owing to the high SPAN loading of 16.37 mg cm⁻². After the introduction of 10 wt% multi-walled carbon nanotubes as a conducting agent, the SPAN disk electrode exhibited excellent cyclability while maintaining a high energy density. This strategy offers a potential candidate for Li/S batteries with high practical energy densities.

A simple synthesis procedure to prepare bulk-type SPAN electrodes toward the realization of Li/S batteries with enhanced practical energy densities.

Evoking High Donor Number-assisted and Organosulfur-mediated Conversion in Lithium-Sulfur Batteries

The solution-mediated behavior of lithium-sulfur (Li-S) batteries presents a wide range of opportunity for evaluating and improving the performance at practical lean-electrolyte conditions. Here, we introduce methyl trifluoroacetate (CH₃TFA) as an additive to the Li-S electrolyte to evaluate the joint effects of two distinct strategies: high donor number solvents/salts and organosulfur-mediated discharge. CH₃TFA is shown to react with lithium polysulfides in-situ to form lithium trifluoroacetate (LiTFA) and dimethyl polysulfides. We find that both the methyl group and trifluoroacetate anion considerably enhance Li-S discharge behavior over the course of cycling, though they have distinctly beneficial effects. The TFA anion impacts solution coordination behavior, improving polarization and discharge kinetics during cycling. Meanwhile, the derivatization to dimethyl polysulfides improves the solubility of intermediate species, enhancing overall utilization under lean-electrolyte conditions. CH₃TFA thus represents a new class of additives for Li-S batteries, enabling an in-situ systematic molecular engineering of intermediate species for improved performance.